The genus Chlamydia comprises the species Chlamydia abortus, Chlamydia pneumoniae, Chlamydia psittaci, Chlamydia pecorum, Chlamydia felis, and Chlamydia caviae. Diseases caused by bacteria belonging to the genus Chlamydia are the following. Chlamydia pneumoniae causes acute or chronic bronchitis and pneumonia in humans and in some cases otitis media, obstructive pulmonary disease and pulmonary exacerbation of cystic fibrosis. It has also been associated with Alzheimer's disease, atherosclerosis, asthma, erythema nodosum, reactive airway disease, Reiter's syndrome and sarcoidosis in humans. Morever, Chlamydia pneumoniae causes respiratory disease in koalas. Chlamydia pecorum strains characterized so far have been limited to mammals, but not to a specific host family. They are serologically and pathologically diverse. The organism has been isolated from ruminants, a marsupial and swine. In koalas, C. pecorum causes reproductive disease, infertility and urinary tract disease. It has been a major threat to the Australian koala population. In other animals C. pecorum causes abortion, conjunctivitis, encephalomyelitis, enteritis, pneumonia and polyarthritis. Chlamydia felis is endemic among house cats worldwide. It causes primarily conjunctivitis and rhinitis. Chlamydia caviae comprises five known isolates, all isolated from guinea pigs. The natural infection site is the mucosal epithelium of the conjunctiva where a non-invasive infection is established. However, it is possible to infect the genital tract of guinea pigs eliciting a disease that is very similar to human genital infection. Chlamydia abortus strains are endemic among ruminants and efficiently colonize the placenta. Chlamydia abortus is the most common infectious cause of abortion in sheep, where the disease is known as ovine enzootic abortion (OEA) or enzootic abortion of ewes (EAE) in countries of Northern, Central and Western Europe. Enzootic abortion in goats is similar in severity to that occurring in sheep, although the spread and economical impact across Europe is less clear because of the lack of epidemiological data. The disease can also affect cattle, swine and horses but this is thought to occur to a much lesser extent. Sporadic zoonotic abortion due to C. abortus has been confirmed by analysis of isolates from women who work with sheep and goats. Chlamydia psittaci produces avian respiratory infections and is a serious threat to industrial poultry production. Additionally, it causes epizootic outbreaks in mammals and respiratory psittacosis or parrot fever in humans.
Protective immunity to Chlamydiaceae (Including the genus Chlamydia) that is observed in animals previously exposed to the pathogen is believed to be effected primarily through the action of CD4+ T helper type 1 (Th1) lymphocytes, CD8+ T lymphocytes, mononuclear phagocytes, and cytokines secreted by these cells (Cotter et al., 1995; Su and Caldwell, 1995; Beatty et al., 1997; Cotter et al., 1997; Johansson et al., 1997; Su et al., 1997; Wiliams et al., 1997; reviewed by Kelly et al., 2003).
Initial attempts to develop an effective vaccine for controlling both animal and human chlamydial infections began with the use of inactivated or live whole organism preparations in the 1950s, e.g. for C. abortus in sheep. In general, such preparations offered a reasonable level of protection, although they have been more successful in protecting animal infections than human infections (Vanrompay et al., 2005).
During the 1960s unsuccessful attempts were made to develop inactivated and live vaccines against C. trachomatis using both human and non-human primates. These vaccines reduced disease in some individuals but they enhanced disease in others resulting from stimulation of enhanced delayed-type hypersensitivity (DTH) response. Therefore, the use of whole organisms for developing human chlamydial vaccines was essentially abandoned.
In the early 1980s an attenuated strain of C. abortus was developed as a live vaccine and is one of the 5 commercially available vaccines in Europe and the USA, the other four being inactivated whole organism based vaccines (Longbottom and Livingstone, 2006). These commercial live-attenuated and inactivated vaccines offer good protection against OEA and significantly reduce the shedding of infective organisms, a factor important in limiting the spread of infection to other animals. However, concerns remain over the safety of using live-attenuated vaccines. There may also be a risk of the attenuated strain reverting to virulence, thus having the potential to cause disease and abortion in the vaccinated animal. Furthermore, the vaccine cannot be administered during pregnancy or to animals being treated with antibiotics limiting its use. In contrast, the inactivated vaccines can be administered to pregnant ewes, although care must be taken in handling and administering these vaccines as they are adjuvanted with mineral oils, which have the potential to cause tissue necrosis if accidentally self-injected. The only other animal chlamydial vaccines, which are commercially available are for C. felis infection in cats (Longbottom and Livingstone, 2006). Although vaccination is successful in reducing acute disease, it does not, however, prevent shedding of the organism and therefore chlamydial spreading in the population nor does it prevent re-infection. Following the identification of the major outer membrane protein (MOMP) as a structurally and immunologically dominant protein vaccine research largely focused on this protein. A certain level of protection has been achieved with COMC (chlamydial outer membrane complex) preparations, in which MOMP constitutes 90% or more of the protein content, using the guinea pig and mouse models for C. trachomatis genital tract infection, and in a mouse toxicity test for C. felis infection (Sandbulte et al., 1996; Pal et al., 1997). Studies on MOMP of C. psittaci were performed e.g. by Tan et al., 1990, Sandbulte et al., 1996 and Verminnen et al., 2005.
DNA vaccination, mimicking a live vaccine, creates protective CD4+ as well as CD8+ responses but antibody responses are low (Verminnen et al., 2010). Moreover DNA vaccines are still too expensive (especially for poultry) and the public is not (yet) ready to consume products from DNA vaccinated animals (in the case of C. psittaci eggs/meat).
Until now, completely safe and effective Chlamydia vaccines are still not available.
The present invention comprises an innovative vaccine that creates both optimal humoral and cellular immune responses by combining B cell and CD4 Th2 cell epitopes (humoral) and CD4 Th1 and CD8+ cytotoxic T cell epitopes (cellular) in a vaccine. In contrast, former and current studies on Chlamydia vaccine development are focusing on cellular responses only (CD8 and CD4 Th1), as they are believed to be crucial to protection against this obligate intracellular pathogen (Su and Caldwell, 1995; Morrison et al., 2000). Moreover, due to the Th1/Th2 paradigm (both responsible for different types of protective responses) vaccine development against infectious agents focuses on creating either a Th1 or Th2 response (Th1 or Th2 polarized vaccines). Thus, the construction of a non-polarized vaccine, deliberately inserting Th1 as well as Th2 epitopes is highly unusual and new as Th1 and Th2 cells act differently and even opposing.
The present invention relates to selected protective B- and T- (Th1 and Th2) cell epitopes of an immunodominant protein (the major outer membrane protein or MOMP). Such protein-based vaccines can be used against an infection with a species of the genus Chlamydia. These peptide sequences do not cause immunopathological reactions nor immunosuppressive T cell responses. Reversion to virulence is not applicable, thus enhancing the safety for both animals and humans. The epitopes can be used in any suitable vector, preferably a vector which: a) can be used in the presence of species-specific maternal antibodies and b) allows easy and cost effective vaccine mass production. Moreover, and surprisingly, the present invention demonstrates that both the cellular- and humoral immune response are required to protect against an infection with a species of the genus Chlamydia. 